This invention relates generally to manufacture of electronic components, and more specifically to manufacturing of inductors.
At least one type of Inductor includes a conductive wire wrapped around a core, sometimes referred to as a drum. The wrapped wire is commonly referred to as a coil, with each end of the coil being referred to as a lead for coupling the inductor to an electronic circuit. A shield is disposed around the coil, and consequently around the core, for isolation of the coil from electromagnetic fields which could induce undesirable voltages in the coil, as well as to mechanically protect the coil from unintentional contact and environmental conditions during manufacture, assembly, and installation of inductors to printed circuit boards and circuitry. As spacing between the coil and the shield can affect open circuit inductance and bias (an open circuit inductance with DC current) of an inductor, centering of the coil to maintain a consistent spacing between the coil, wound on the core, and the shield is important to the consistent manufacture of reliable, high quality inductors. Use of mechanical tooling to center the coil, and subsequently the core, within the shield is difficult and expensive to implement.
Manufacturing processes for inductors, like other components, have been scrutinized as a way to reduce costs in the highly competitive electronics manufacturing business. Reduction of manufacturing costs are particularly desirable when the components being manufactured are low cost, high volume components. In a high volume component, any reduction in manufacturing costs is, of course, significant. Manufacturing costs as used herein, refers to material cost and labor costs. It is possible that one material used in manufacturing a component, may have a higher cost than another material, but the labor savings more than makes up for the increase in material costs. It is also possible that the opposite is true in other component manufacturing circumstances.
Conventionally, to avoid mechanical tooling costs in inductor fabrication, an adhesive tape has been used as a spacer between the core and the shield. A liquid epoxy adhesive is then externally applied to the inductor to mechanically bond the core to the shield. Application of the external adhesive adds a manufacturing step and associated expense to the inductor fabrication process. Additionally, a smooth and polished surface of the spacing tape can undesirably compromise the bonding between the tape and the shield, and because it is difficult to externally apply adhesive to an entire surface area of the core within the shield, only a portion of the core surface area is bonded to the shield. Poor bonding of the core to the shield can undesirably affect performance of the inductors.
In an exemplary embodiment, a method for fabricating an inductor includes the step of wrapping an epoxy tape around a perimeter of an inductor core, positioning the wrapped core into a shield, and reflowing the epoxy tape to form a uniform bond between the core an the shield.
More specifically, the epoxy tape includes a layer of structural adhesive film laminated to an adhesive layer. The structural adhesive film is affixed to the perimeter of the core, and the core is bonded to the shield by heating the adhesive layer of the epoxy tape to a transition temperature to melt the adhesive layer, and curing the adhesive layer to a solid state bonded to the shield.
The epoxy tape ensures centering of the coil and core within the shield and further ensures a complete bonding between the core and the shield, thereby improving inductor performance and reliability while avoiding conventional manufacturing steps.